aws-ecs: `ContainerImage.fromEcrRepository` should be `tagOrDigest`

### Describe the issue

The underlying `EcrImage` constructor has the correct naming `tagOrDigest` since most use the helper static method the name and documentation should be updated there is as well.

https://github.com/aws/aws-cdk/blob/v2.144.0/packages/aws-cdk-lib/aws-ecs/lib/images/ecr.ts#L22

### Links

https://github.com/aws/aws-cdk/blob/v2.144.0/packages/aws-cdk-lib/aws-ecs/lib/container-image.ts#L22
https://github.com/aws/aws-cdk/blob/v2.144.0/packages/aws-cdk-lib/aws-ecs/lib/images/ecr.ts#L22

Start with packages/aws-cdk-lib/aws-ecs/lib/container-image.ts and packages/aws-cdk-lib/aws-ecs/lib/images/ecr.ts at the linked declarations. Compare the parameter name and documentation in both locations, then update the helper so the naming matches EcrImage; done means the public name and its documentation consistently use tagOrDigest.

Written by the indexing model from the issue text.